One of the limitations in the speed with which a programmed power supply can operate is the rate at which the output capacitor can be discharged when a reduction in output voltage is called for. When the capacitor is discharged through a shunt resistor, the rate of discharge decreases as the voltage across the capacitor falls; and when the capacitor is discharged through the collector-to-emitter path of a transistor, the current must be limited to the maximum that can be drawn at the higher initial voltage without exceeding the rated safe operating area of the transistor.